1. Field of the Invention
The invention relates to a lithium ion cell, comprising a positive electrode which contains a chalkogen (i.e., chalcogen) compound containing lithium, of a transition metal, a non-aqueous electrolyte and a negative electrode which is separator-isolated and contains carbon.
2. Description of the Related Art
It is known from the document J. M. Tarascon and D. Guyomard, Electrochimica Acta, Volume 38, No. 9, pages 1221-1231 (1993) that lithium ion cells of the abovementioned type suffer an irreversible loss of lithium ions after the first charge/discharge cycle, which leads to a 25-50% loss of capacity. The lithium ions are in this case bonded by the active material (which contains carbon) of the negative electrode and are no longer available for charge transport. In order to compensate for this loss of capacity, it has already been proposed to fit a lithium ion reservoir by adding n-butyllithium or lithium iodide to the negative electrode. Losses of lithium ions which are lost by reaction with the electrolyte, impurities or changes in the chalkogen compounds are also intended to be compensated for in this way.
European Patent Document EP-A-201038 proposes that the positive and/or negative electrode be doped with lithium ions. After this, the discharge capacity of the positive electrode is preferably dimensioned to be 1.1 to 3 times greater than that of the negative electrode. Furthermore, it is known from the document U.S. Pat. No. 5,162,176 for the negative electrode, which contains carbon, to have lithium added in advance, amounting to from 1 to 6% by weight of the electrode mass, in order to compensate for the irreversible lithium loss. The known lithium ion cells are sensitive to decomposition reactions when handled in air, as a result of lithium being added to the active materials of the electrodes. Complex and costly drying room methods must be used to manufacture them. The cell which is known from the document U.S. Reissue Pat. No. 33,306 also has the disadvantage that the lithium metal, which is in direct contact with the anode material that contains carbon, leads to a compound which is very highly reactive and involves an increased production cost.